Steel City 1-Gang 4 cu. in. Round Ceiling Box 36115C-25R - The Home Depot
Steel-City 56111-CFB 4" Steel Round Ceiling Fan Box, 1/2" Deep, 6 cu.in. w/ 1/2" KOs | Crawford Electric Supply
RACO 6261 Deep Round Cast Iron Floor Electrical Box, with v(4) 3/4-Inch Side Knockouts and 3-3/4-Inch Minimum Depth of Pour - Electrical Boxes - Amazon.com